Undifferentiated pleomorphic sarcoma (UPS) is a rare type of cancer that begins mostly in the soft tissues of the body. Soft tissues connect, support and surround other body structures.

UPS usually occurs in the arms or legs. Less often it can happen in the area behind the abdominal organs (retroperitoneum).

The name undifferentiated pleomorphic sarcoma comes from the way the cancer cells appear under the microscope. Undifferentiated means the cells don't look like the body tissues in which they develop. The cancer is called pleomorphic (plee-o-MOR-fik) because the cells grow in multiple shapes and sizes.

Treatment for UPS depends on the location of the cancer, but often involves surgery, radiation and drug treatments.

UPS used to be called malignant fibrous histiocytoma.


Undifferentiated pleomorphic sarcoma symptoms depend on where the cancer occurs. It most often happens in the arms and legs, but it can happen anywhere in the body.

Signs and symptoms may include:

  • Growing lump or area of swelling
  • If it grows very large, there may be pain, tingling and numbness
  • If it occurs in an arm or leg, there may be swelling in the hand or foot of an affected limb
  • If it occurs in the abdomen, there may be pain, loss of appetite and constipation
  • Fever
  • Weight loss

When to see a doctor

Make an appointment with a doctor if you develop any persistent signs or symptoms that worry you.


It's not clear what causes undifferentiated pleomorphic sarcoma.

Doctors know this cancer begins when a cell develops changes in its DNA. A cell's DNA contains the instructions that tell a cell what to do. The changes tell the cell to multiply rapidly, creating a mass of abnormal cells (tumor). The cells can invade and destroy nearby healthy tissue. In time, the cancer cells can break away and spread (metastasize) to other parts of the body, such as the lungs and bones.

Risk factors

Factors that may increase the risk of undifferentiated pleomorphic sarcoma include:

  • Older age. This cancer tends to occur in adults older than 50, though it can occur at any age.
  • Previous radiation therapy. Rarely, this cancer can develop in an area of the body that was previously treated with radiation therapy.

Most people who develop undifferentiated pleomorphic sarcoma have no known risk factors, and many people who have risk factors never develop the cancer.